Means for finishing helical forms



y 936 B. w. TWYMAN I Y 2,040,347

MEANS FOR FINISHING HELICAL FORMS Filed Sept. 29, 1954 INVENTOR F.1d 'BY' ATTORNEYS Patented May 12, 1936 UNITED STATES PATENT OFFICE MEANS FOR FINISHING HELICAL FORMS Application September 29, 1934, Serial No. 746,029

4 Claims.

This invention relates to means and methods for manufacturing worm cams and screws.

It is the primary object of this invention to provide a substantially frictionless burnished threadway in a worm cam or the like by a new and improved burnishing method in which a piece of screw threaded shafting is properly piloted and driven axially through a series of adjustably mounted balls, each of which are successively mounted in a gradually decreasing radius measured from the axis ofthe thread being burnished, so that the last ball in the series will give the finished and burnished thread the suitable working clearance essential to its further commercial use as an article of manufacture.

It' is a still further object of this invention to provide a manufacturing process and tool for the production of such worm cams, screws and the like, which shall be both simple and economical whether used in quantity production or for small amounts.

In the drawing:

Figure 1 is a vertical cross section through the thread burnishing device.

Figure 2 is a longitudinal cross sectional view taken on the line 2-2 of Figure 1.

Like parts are identified by the same reference characters throughout the several views.

This application is a companion to my application Serial No. 717,177.

In Fig. 1 the apertured burnishing housing comprises a rigidnut fitting I having a series 'of radially disposed threaded apertures 2 corresponding to the pitch of the thread 3 on the worm cam 4 movable therethrough. A series of adthread and are economical and easily replaceable in the sockets 6. For other purposes any other form of hardened tool might be made integral with, or to be mounted in the adjusting bolts 5.

A cylindrically bored pilot housing I serves as a guide for the worm cam 4 which it preferably (but not necessarily) engages after the cam is fed axially past the balls I. The work (worm cm I) and the tool fitting (the burnishing device) may be moved with reference to each other in any one of anumber of ways. For example, the burnishing device may be set with its axis upright and a worm cam blank of any desired length, with previously roughly machined thread, 5

may be impelled, as by a drill press, by axial pressure through the burnisher to finish the thread. Preferably, however, each finished length of worm cam is provided with an internal bore and a longitudinally extending groove and is splined to a quill H such as may be mounted conveniently in a slide I4 of a screw machine.

The quill II, in this organization, is held stationary, and the guide fitting l0 and nut I are rotated in the chuck l5 of a screwmachine spindle l6 which is tubular. Each blank is thereby screwed into and through the burnishing appliance so that the'rough thread initially formed on the blank will be finished and burnished by theball tools I, and each blank in turn pushes '2 its predecessor out through the hollow spindle.

It is therefore immaterial whether the work and thetool be moved with reference to each other under axial pressure or rotative pressure. It has been found convenient, however, to rotate the nut as last outlined above and shown in the drawing.

The preferred method of manufacture is as follows:

A piece of sha'fting of proper dimensions. is bored and a keyway browhed therein in the conventional manner. The stock is then placed on a bolt cuttenusuallyon an arbor, and the threads are roughly out, after which the worm cams are trimmed to finished length and bearing surfaces are cut in either end. Thecam is then splined to a quill held stationary on a multiple turret lathe or screw machine and driven axially or screwed through the burnishing tool. At the completion of this operation the cam is thoroughly burnished. The rough thread might, for example, have the identical arc of the ball or complementary thread which is ultimately to be used-in mesh therewith. In the burnishing operation eachsuccessive burnishing ball will be I claim: I 1

1. A thread burnishing device comprisingthe combination. with a sleeve guide for a rough threaded worm cam blank, of a series or ball tools positioned in the path of a worm cam advancing beyond said blank and respectively offset on a pitch corresponding to the rough thread thereof, and means supporting said ball tools at successively decreasing radial distances from the .axis upon which said blank moves beyond said guide.

whereby said tools will be successively eflective in burnishing and enlarging the .thread of the blank. Y

2. A thread burnishing .device comprisinga set o1 balls positioned on a helical path corresponding in pitch to the thread to be burnished at progressively decreasing radial distances from the axis-of such path, andmeans supporting said balls in the positionsaforesaid.

3. A thread burnishing device comprising a set 01 balls positioned on a helical path corresponding in pitch to the thread to be burnished at progressively decreasing. radial distances from the axis of such path, and means supporting said balls in the positions aforesaid, said means com-- ially spaced from each other in positions to act successively upon the work, each of such tools being engageable with asingle thread and each being substantially circular in crosssection whereby to be smoothly rounded in the directions 'oi' engaging and leaving all the surface of the work traversed thereby.

B. wIcKimFE I'WYMAN.

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